Mankind has an insatiable desire to communicate. This demand has spurred on the development of a great variety of communications technologies—both wired, in the form of telecommunications and data networks, and wireless, such as cellular, microwave and satellite systems.
Making all these systems work together has become a daunting challenge. Back when there was only one dominant service provider—the Bell System in the U.S. and Canada—it was relatively straightforward to add a new technology to a fairly uniform network. In the case of wireless systems, the upgrades often involved a complete swap-out of the existing RF (radio frequency) units. But, the limited number of units, by today's measures, and fixed transceiver characteristics (e.g., a single modulation type), made migration far easier to plan for then than now.
Today, if a service provider wants to implement a wireless link using multiple modulation schemes at varying frequencies, it must typically resort to redundant componentry to cover the differing forms of communication. For example, the main receiver path for a microwave RF unit is traditionally equipped with band pass filters, whose bandwidth is equal or slightly larger than that of the signal to be processed. This capacity dependent filter determines the sample of the receiver path used to derive the AGC (automatic gain control) loop control voltage; the RSL (received signal level) strength indication is similarly derived. Since bandwidth tunable IF (intermediate frequency) filters are expensive and immature technology, the only practical way, until our invention, in which to implement a microwave RF unit that is wide-range (by which we mean multi-capacity, multi-bandwidth, and multi-frequency) would require a bank of IF bandpass filters. However, such filter banks, for use across many different bandwidths, arc not cost effective. They also occupy significant space in the RF unit, which defeats a key objective of keeping the RF unit small and compact.
A different kind of problem exists when with trying to implement the transmitter path in a wide-range microwave transceiver. In order to achieve a wide dynamic range, e.g., 40 dB accurate power control-at microwave frequencies, most current designs rely on open-loop calibration methods. These typically require the RF unit to be calibrated as a whole unit, leading to complexity in the overall test setup, increased costs, and increased test times.
In both cases, current designs fail to adequately address the problem created by the needs of service providers to more frequently change their network configurations. Whether driven by advances in technology, or changing customer requirements, a more flexible RF unit design is needed to avoid a complete unit swap-out as new capacity/bandwidth/frequency technologies are implemented for a given link. Thus, there is a need for a better microwave RF unit design, one which allows for flexibility and ease in implementing multiple performance criteria (e.g., capacity, bandwidth, and/or frequency) in a low-cost manner, while still meeting all desirable and mandated regulatory specifications for the selected types of communications.